Graining or abrading lithographic plates or the like by centrifugal blast of wet slurry



5 Sheets-Sheet l INVENTOR.

OTTO E. ZAHN LIKE BY CENTRIFUGAL BLAST 0F' WET SLURRY wwww Filed March 17, 1949 HN 2,532,136 GRAJZNING 0R ABRADING LITHOGRAPHEC PLATES 0R THE LIKE BY CENTRIFUGAL BLAST 0E WET SLURRY Filed March 17; 1949 5 Sheets-Sheet 2 INVENTOR. 077-0 E. ZAHN BY M, m 7*- 0. E. ZAHN 9 GRAINING OR `BRDING LITHOGRAPHIC PLATES 0R THE LIKE BY CENTRIFUGAL BLAST OF' WET SLURRY Filed March 17, 1949 5 Sheets-Sheet 5 INVENTOR.

5] OTTO E. ZAHN MM YM ATTORNEYS.

E. ZAHN GRAINING 0R ABRADING LITHOGRAPHIC PLATES OR THE Wmv. 2%, W5@ Q LIKE BY CENTRIFUGAL BLAST 0F WET SLURRY Filed March 17, 1949 5 Sheets-Sheet 4 INVENTOR. 0770 E. ZAHN TTOHNEYS.

E. ZAHN Nov.. 28, 1950 2,532,136 GRAINING OR ABRADING LITHOGRAPHIC PLATES OR THE LIKE BY CENTRIFUGAL BLAST OF' WET SLURRY Filed March 17, 1949 5 Sheets-Sheet 5 PRESSURE TANK f TRAVEL V `E mZ `N EE. 4m W0 T .IT .1A 0

Y B am n Qrw Wl A y.. i @in \\\\lv O 1/ w o m Patented Nov. 28, 1950 UNITED STATESu A'rENT OFFICE Gtto E. Yahir,` Mishawaka,

Ind., assigner to American Wheelabrator & Equipment Corporation, Mishawaka, Ind., a corporationof Dela- Application March 17, 19119, Serial No.81,896

11 Claims.

The invention relates to the abrading orgra-ining of surfaces and, more particularly, to the art of graining lithographie sheets.

lit` is common practice to grain or roughen the surfaces of metallic sheets or plates for lithographie purposes, to make the liquid receptive `areas accept and hold moisture more easily and uniformly.

An object of the invention is to produce a method, and machine, ior graining such plates more quickly and less expensively than is possible with present commercial practices.

According to a preferred manner of practicing the invention, the sheet is abradedby the `use of a slurry comprising a suitable vehicle, such as water, in which is suspended a suitable graining or abrading agent, such as fine iron grit. The slurry is fed into a blast Wheel which discharges the material at high velocity against the surface of the sheet.

According to a preferredform, the machine for practicing the invention comprises, essentially, a vertical cabinet in which an elevator1 isreciprocated up and down. On the elevator is mounted a rotary turntable. On the turntable is mounted a plurality of cylindrical plate holders or shells. Each plate holder has devices forwsupporting cylindrical plates to be grained. Mounted inthe cabinet, and concentrically of the elevator, is a horizontally disposed, non directional blast wheel. The blast wheel is adapted to discharge a slurry horizontally, and uniformly about its entire periphery, against the cylindrical plates, as they are moved back and forth in the path of the blast. Suitable means for drivingthe elevator are provided, including a hydraulic servomotor arrangement. Suitable means is also provided for feeding and circulating the slurry and for keeping it stirred up. Such circulatory system comprises an upstanding feed pipe feedingvinto the open center of the blast wheel. The spent slurry drops to the bottom of the cabinet where it is caught in a sump. The spent slurry is drawn off by a circulatory pump which feeds the upstanding feed pipe. Suitable stirring pipes are branched off from the feed pipe to bypass part of the slurry back into the sump, the discharge being in such direction as to keep the slurry strredup. i

The invention also consists `incertain new and original features and combinations hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this .invention will he particularly pointed out in` the ulczlairns appended with the accompanying drawings forming a part hereof, in which:

Fig-` 1 is ,a vertical central section, partly in elevation, of the complete machine;

Tig.` 21is a Atopplan View of the complete machine, with certain of the piping omitted;

Fig. 3 is a plan Vsection along line 3-3 of Fig. l, taken through the blast wheel;

Fig. 4 `is an enlarged half section, in perspective, of the reciprocating elevator;

Fig. 5 is a fragmentary detail section, taken along .line .tHE of Fig. 4, showing the construction of the `rotatable carriage or turntable, in relation to the lower supporting ring of the ele- Vator;

Fig.` 6 is a plan view of oneof the plate holders;

Figa? is `anfelevation of a plate holder, viewing it from the inside;

Fig, 8 .is a fragmentary section taken along line fia-S of Fig. '7, showing a releasable holding member for thetopedge of` theplate to be processed;

Fig. 9 isa, fragmentary section taken on the line 9 9 of Fig. 7.showing spring clips along bottom ring of theplate holder which hold the work plate in place;

l'ig.` 1G is a schematic view illustrating the hydraulic system utilized for reciprocating the elevator; and

Fig. ll isa detail plan section talren along line H-ll of Fig. .10,showing the `ball detent for yieldably maintaining upper` and lower position of pilot valve actuator rod.

In the following deseriptionand in the claims, various details will be identified by specific namesfor convenience, but they are intended to be as generic in their application as the art will permit.

Like referencecharacters denote like parts in the several figures of the drawings.

En `the. drawings `accompanying and forming part ofthis specification, certain specific disclosureof 4.the invention. is made for purposes of explanation, but it will be understood that the details may be modified in various respects` Withfu `out. departurefrom the broad aspect of the .invention.

The machine .will rst be described generally.

The Ymachine comprises, `in generaha `vertical cylindrical ,tank-.or cabinet it inwhich ismount.-

eel-the centrifugal blast wheel l i the blast wheel -isdriven by `the-.electric .motor l2 secured in mo.-

tor housing It. Slurry is fed upwardly to the center of the blast wheel il by a feed pipe I4; pipe lil receives discharge from a centrifugal slurry pump l5, arrows i6 indicating direction of slurry flow. Spent slurry is caught in the bottom of the sump il whence it ows back into slurry pump I l.

Two lithograph plates l are mounted in two, half-cylindrical, plate holders I9 (see also Figs. 6, '7 and 9) which are supported on a rotary turntable 2). The turntable '2b is mounted on four rollers 2i which in turn are mounted at the bottom of an elevator cage 22.

The elevator cage is supported by two lines or cables 23 running over pulleys 24, 25 mounted at the tcp oi the cabinet; these lines extend to a power-driven, vertically-movable yoke 26 (see Fig. 1G) for reciprocating the cage vertically. The yoke 26 is driven by a hydraulic engine comprising a cylinder 2l having a piston 28. Hydraulic pressure is supplied alternately to the ends of the cylinder by a suitable hydraulic servomotor mechanism.

Thus, by driving the blast wheel to discharge slurry, and by vertically reciprocating the elevator cage, all parts or" the lithographie plates may be subjected to the action of the slurry and suitably grained.

The machine will now be described more in detail.

As shown particularly in Figs. 1', 2 and 3, the cabinet lil has an upright cylindrical coniiguration; it comprises a generally cylindrical wall 29 suitably supported by structural frame members on a base 35. The structure includes the vertical elevator rails 3l. Near the bottom is a dished wall il forming a sump to hold the spent slurry. The interior of the cabinet is accessible through a large .Front opening closed by two swinging doors 32. The doors are hinged to the cabinet near the elevator rails 3! by a series of hinges The doors are held closed by a series of door clamps height of the opening is made slightly smaller than the height of the doors 32. The doors are opened to insert and remove the lithographie plates and are closed to coniine the slurry to the inside of the cabinet.

The cylindrical motor housing I3 depends from the top of the cabinet, forming an annular space with the side walls of the cabinet to permit telescopic movement of the elevator, as discussed below. The bottom of the motor housing i3 is closed and from it depends a bearing tube 31. The bearing tube il is strengthened by a series of triangular gussets 38 secured to the bearing tube and to the bottom of the motor housing 3.

The electric motor i2 is suitably supported in the housing it. A direct coupling l5 connects the motor shaft and extension shaft 44. Shaft is journaled in the bearing tube 3l, A screen 39 provides a Ventilating opening for the motor. The rest of the motor housing is enclosed to protect it from the slurry.

Supported on the lower end of the extension shaft M. is the horizontal blast wheel II. This wheel may be of any suitable construction adapted to deliver a horizontal blast for the entire 360 of its circumference.

In its present form, the blast wheel lI is made up of a lower plate il and an upper plate 42 to which the hub i3 is secured. The hub is suitably keyed on shaft ll. Between plates 4l and 42 are a series of radial blades ll (Fig. 3) extending from a point spaced from the center to the periphery of the plates. These blades are suitably clamped between the plates 4|, 42 by suitable clamping devices indicated by 41. A discharge tting 48, supported at the top of slurry feed pipe Ill, passes through a concentric hole in the bottom of lower plate 4| into the open hub of the wheel.

It will be understood that, as slurry is fed under pressure upwardly through feed tube I4 and as the blast wheel is rotated at centrifugal discharging speed, the slurry will be fed equally to the inner ends of the several blades 46. The blades 45 pick up the slurry and discharge it at high speed continuously, throughout the entire circumference of the wheel, against the lithographic plates, as explained more fully below.

Referring now more particularly to Figs. 4 to 9, the elevator cage 22 comprises an upper ring 50 and a lower ring 5| suitably connected by pairs of Vertical tie strips 54. The upper and lower rings are suitably made by bending channel stock as shown.

The upper ring 50 connects with guide shoes 52 having slots embracing the elevator rails 3|. Similarly, the lower ring 5| has lower shoes 53. As shown, these shoes connect the upper and lower rings with the vertical tie strips 5d. The upper shoes 52 have eye bolts 55 for connection to the supporting cables 23.

The lower ring El has four rollers ZI for supporting the turntable 26. Turntable 20 is made up of a track member 58 having an annular groove in which the rollers 2| ride. Secured to track 58 is a flat ring 59; ring 59 is secured to an upstanding collar El by a series of radial spacing strips G0. Track member 58, dat ring 59, spacing strips 6U and collar GI are suitably welded together. Four retaining angles B2 are supported by adjusting bolt assemblies '53 secured to lower ring 5|. These angles are spaced slightly from the turntable and are for the purpose of preventing the turntable 2) from being tipped or lifted off the rollers 2|.

Removably resting on the turntable 2|) are the two semi-cylindrical plate holders I9 (see particularly Fig. 9). As shown in Figs. 6 and 7, each plate holder I9 comprises a curved steel sheet 65 having its vprtioal margins suitably reinforced by angle strips B6. Handles 6l are provided for lifting the plate holders ofi" the turntable 2.

For removably supporting the lithographic strips to be grained, the plate holder I9 is provided with a lower holding ring '58; the upper edge of ring E8 is suitably oiset from the cylindrical plate 65 to provide a space in which the lithographic plate is inserted. A series of U-shaped spring clips 69 engage in this annular space to facilitate insertion of the lithographie plates in position on the holder plates and the removal therefrom.

The upperl edge of the lithographie plate is held in position by a plurality of T-clamps 'l0 (see also Fig. 8). Each of these clamps comprises a shank l! and a cross piece 'I2 suitably secured thereto, and a knurled nut 'I5 threaded on the shank 'l I. A spring 73 acts between a washer i4 and nut l5. The plate holder I9 has a series of slots l5 at different levels through which the T-clamps are inserted, depending upon the height of the lithographie plates. It will be understood that the cross piece I2 is inserted through the particular slot 'I6 and the T-clamp turned to engage over the upper edge of litho plate I 8, as indicated especially in Fig. 8.

The slurry circulatory system is as follows. Mounted at the side of the cabinet, and down near the bottom, is a centrifugal slurry` pump` I; pump I5 is direct coupled wit-han electric drive motor 18. The pump I5 dischargesthrough` piping 80 in the direction of arrows IISV to `the .riser pipe I4.

Intersecting the riser pipe i |4 are a series of bypass pipes 8|. These pipes project downwardly at` an angle to the `riser pipe I4 and terminate in open elbows, as shown particularly in Figi. Itis preferred to use three equally spaced stirring pipes 8i; only two pipes are shown for simplicity of illustration.` Any suitable number may be used, the object being to bypass some of the slurry back into the slurry tank or sump |1 to keep the slurry stirred iup, to prevent solid particles from settling out from the liquid vehicle.

The discharge pipe 8,0 connects, with a drain pipe 83 through a normally closed gate `valve 84; valve 84` is suitably controlled by a lever 85. An overilow pipe 82 connects with drainpipe 83 to limit the height of the slurry in the bottom of the` cabinet.

The bottom of sump I1 is provided with an outlet communicating with the inlet of slurry pump I5; the outlet is covered by a screen 19.

The slurry circulates as follows. The pump |.5` draws slurry from the sump I1 through screen 1,9, discharges it through pipe 80 into riser pipe I4. The pipe I4 feeds the wheel II. The rotating wheel discharges the slurry against the work, whence the spent slurry drops to the bottom of the cabinet where it is re-circulated- Part of the slurry is bypassed through the stirring pipes 8| whose outlets are directed at such a tangential angle with respect to the circular sump as to keep the slurry stirred.

While the blast wheel I.| is discharging slurry, the elevator cage is being reciprocated up and down to expose all partsequally of the litho plate to the graining action of the slurry. The elevator is shown in the gures on its` way up.

The elevator cage 22 is reciprocated automatically in any convenient manner. In the form shown, a standard hydraulic servomotor mechanism is used which is especially adapted for this particular purpose. The servomotor mechanism comprises a cylinder 21 suitably mounted at the side of the. tank by upper and lower brackets 88 and 8,9. See also Fig. l0 where the parts are shown somewhat diagrammatically. to facilitate description and understanding of the invention.

Stationary slide rods 98 connect bracket 89 and a lower bracket 9| also secured to the tank. A yoke 28Hslides vertically. on rods 9 0; theyoke is connected to piston` rod` 92V secured to piston 28 slidable in cylinder 21. Turnbuckles 93 connect the` lines or,` cables 23 to the yoke 26,. These cables pass over the pulleys 24 and 25 journaled at the top ofthe tank and down into the tank, as indicated particularly in Figs. l and 2. In Fig. 10 the parts are shown with the hydraulic fluid forcing piston` 28 downwardly, which in turn pulls.

cage 22.` upwardly.`

The control mechanism includes a control rod 94 slidable infbracket 9 Iand in an upper bracket 95` also secured tothe side of the tank. A balance spring 95 balances `the weight ofthe .rod 94. Rod 94 carries adjustable collars 91v and 98'which are engagedby. yoke 29to limit the stroke of the servomotor. 21, Z8; Collars` 91 and 9B are ad-` justablelon actuating` rod,i 94 to limit the stroke from.substantiallymaximum position, as shown in.the drawings., t0 a smaller stroke which can be obtainedby. moving the adjustable collars `91 and 9.8 toward-eachother A detent arrangement yieldably holds the conlower position. (Slee also The detent includes a `spring pressed trol rod 94 in upper or Filgrill'.)

ball QQ-Slidablymounted in la `fitting t0lfsecuredf The `bal-l `99- l yieldably" engages "a to bracket 9|=`i pair of notches |00 in actuating `rod 94.` Thus.; when 'yoke' 26 engages loweril collartt, it will. push rod 94 downwardly to cause the bal199 to engage in the upper notch A| 00 to yieldably--hold the--actuatingrod 94 -in lowerpos-ition. Similarly, when yoke ZSengagesupper collar 91, it pushes` rod 941 upwardlyto engage `ball `99 in theV` lower `notch |00to hold the rod 94-in theupperipositi'on.shown in" Fig., 10.

Liquid' tothe `hydraulic motor 21, 2B is admitted through pipesfC` and D.; These pi-pes alternately apply pressure to the ends of` the-cyl` inder` 2 1 simultaneously exhausting theother end" of thecylinder.

Liquid iiow is4 controlled bya foureway pilot valve.l |04 which isoperatedby a `lug |05" secured to. the actuating` rod 94. Pilot valve` |04. is thus operated, between two positions to operate a, standard four-wayinain valve |06 which controlsv the: flow through4 pipes C, and D; as explained below.

As part of "the, hydraulic control system, a hy-` draulic pump. |08; is mountedon a hydraulic tank |091. alongside thecabinet (seeFig 2).' The hy-` draulic pump,4 |08 is driven byan electric` motor |01. The pump draws liquid` from tank through suction pipe I0 and discharges through a pressure relief valve I I to pipe A.` PipeA feeds main. valve l |06. and pilot valve |04, as shown. by theldirection of thearrows in Fig.. l0. Pipe B is. anexhaust. pipe taking liquid from maini'valve |06 and pilotvalve |05, back to tank |09.

Pipe C!` connects the lower end of cylinder 2.1"

andmain. valve |.06`through a throttle valve |2; pipe D connects, the upper end `ofi cylinder` 2 1` and. mainvalve |06lthrough a second `throttle valve, I i3.. These throttle valves.` areof standard. construction., They may, be adjusted to variably throttle the hydraulic fluid being` fed to the cylin der 21.r and in this way` the` speed of `movement of theservomotor 21, 28 may be controlled. Regardless. of throttle adjustment, the valves. and ||2 always pass freelyaexhaust fluid... Thus, byadjustinglthrottle valves |.|2 and |3,.the speed otmovement ofthe servomotor 21.28'may beadjusted.`

Theseveral valves, viz.: pilot valve |04, main valve |.06. and throttle valves ||2, ||3` are of standard construction. It is thought that ltheir. operation willbe obvious from. their following description..

The arrows on the several pipes A,.B,..C. and D indicate iiow of liquid. to.move the piston 28 downwardly, as shown in Fig. 1.0. The pilot valve |04 has previously been operated to the position shown. to place main valve |06.. in the position shown. Liquid,y thus flows through pipe A in the direction of thearrows, through main. Valve |06 to pipe D tothe upper .endof the cylinder 21. EX- haust uid passesfrom the lower end of cylinder 21 through pipe C, main valve l |00 to return pipe B.v

When yoke 26lreaches collar 9 8, it=pushes con. trol rod. 94` downtoengage the `uppernotch |00 with detent ball` 99; This pulls collar |05 down cooperate pilot` valve |04. Thisreverses thefiow through pipes E andF to,r evers e theposition of main valve |06. This causes liquid. pressure i. to b e applied to pipe C to force piston4 28 upwardly and. permits the upper end.. or the; cylinder` 2J.' to exhaust through pipe D.`

7 Operation of machine One method of operating the graining machine is as follows. The slurry motor 18, the hydraulic motor 101 and the blast wheel motor I2 may be all separately controlled.

Assuming that all of the motors are stopped and that it is desired to insert new plates to be grained, the cabinet doors 32 are opened and the plate holders I9 are removed from the cabinet; the turntable facilitates removal. lithograph plates i8 to be grained are set and secured in their plate holders *I9 and the plate holders, in turn, are set on the turntable 20 to form a complete cylinder. The first plate holder is inserted rst; the turntable is turned 180 and the second plate holder is then placed in position. It is only necessary to close the cabinet doors and the machine is ready for operation.

The machine may be started in the following order. The blast wheel motor I2 may be rst started, then the hydraulic motor |01 and the servomotor 21, 28, then the slurry pump motor 18. The lithograph plates may be subjected to the blast of slurry for any desired length of time. The amount of graining is determined by the plate grainer or operator of the machine. Tests have shown that some plates may be grained in as little as three minutes while others take longer.

The machine may be stopped, after a plate is grained, by rst stopping the elevator, then the blast wheel and last the slurry pump using the slurry to brake the wheel.

The control of the elevator speed is set by adjusting the throttle valves H2 and H3. When the valves are opened, the elevator travels faster, and vice versa. The depth of the grain may be controlled in various ways: by slow or fast travel of the elevator, by change from short to longer blades in the blast wheel, or by the number of passes or reciprocations of the elevator.

Thus the invention provides a small, compact machine using a wet process. It grains plates more uniformly, faster, and more cheaply. Tests have shown that desired grain can be obtained from about three or four minutes to about twelve minutes of operation, depending upon whether plate to be grained is a new plate, an albumin plate or a deep etch plate.

The present machine can produce a grain cn zinc, aluminum, copper or stainless steel plates. Any desired grain size can be obtained by changing the size of the abrasive. There is no vibration. All of the fast moving parts rotate and are balanced, and the only reciprocating parts move at slow speed. There is no dust. All of the wet abrasive slurry is contained within the cabinet of the machine.

The type of slurry may be varied according to conditions. Excellent results have been obtained using a very iine iron grit suspended in water with caustic to remove albumin, a rust inhibiter and a wetting agent. However, many of the slurries, that are now used with conventional horizontal, vibrating tray-type lithoplate graining machines, may also be used to practice the invention.

The present machine produces a much more uniform grain than conventional machines; and because of the great uniformity of grain, it has been found that less water is necessary in the printing process which is very desirable because sharper images are produced.

While certain novel features of the invention have been disclosed herein, and are pointed out in the annexed claims, it will be understood that The two I various omissions, substitutions and vchanges may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. In a graining machine, an upright, substantially cylindrical cabinet, a non-directional blast wheel whose plane is substantially horizontal, means `for rotating said wheel, said wheel comprising a plurality of substantially radial blades and having an open center, a feed conduit feeding material to said open' center, means for feeding a slurry of liquid and solid particles to said conduit, an elevator cage having means for supporting the plate to be grained, and means for reciprocating said cage up and down in a path surrounding said wheel to subject substantially all parts of the Work plate to said slurry blast.

2. In a blasting machine, a cabinet, a cage, means for reciprocating said cage axially, a turntable rotatably mounted on said cage, a set of plate holders resting cn said turntable, said plate holders each having means for supporting a plate to be blasted, and means inside said cage for blasting said plates.

3. In a graining machine, an upright cabinet, an elevator cage having shoes, said cabinet having Iguide rails on which said shoes ride, sheaves journaled on the top of said cabinet, lines passing over said sheaves connecting said elevator means connected to said lines for reciprocating said cage up and down, said cage including a lower supporting ring, rollers rotatably mounted on said ring, a turntable having a track member provided with an annular groove riding on said rollers, a set of plate holders resting on said turntable, said plate holders each having means for supporting a plate to be grained, and means for blasting said plates.

1l. In a blasting machine, a cabinet, a motor housing supported from the end of said cabinet, said housing having an open end but otherwise being substantially closed, an electric moto-r in said housing having a shaft passing through the wall thereof, a blasting device on said shaft, a cage, means for supporting the plate to be blasted on said cage, means for reciprocating said cage into the annular space between said motor housing and cabinet wall to expose all parts of the plate to the action of said blast device.

5. ln a lithographie plate graining machine, an upright cabinet, a motor housing suspended from the top of said cabinet, said housing having an open top but otherwise being substantialiy closed, an electric motor in said housing having a depending shaft passing through the bottom thereof, a blast device on said shaft, an elevator cage having shoes, guide rails inside said cabinet on which said shoes ride, means for supporting the plate to be grained on said cage, means for reciprocating said cage into the annular space between said motor housing and cabinet wall to expose all parts of the plate to the graining action of said blast device.

6. n a blasting machine, a plate holder for holding a lithographie plate or the like, said plate holder comprising a cylindrical sheet, a lower holding ring secured to the lower edge of said sheet, the upper edge of the ring being olfset from the cylindrical sheet to provide an annular holding space, the upper end of said sheet having a series of slots at different levels, a series of clamps each comprising a shank and a head, each said shank having an abutment and a spring surrounding the shank engaging said abutment, whereby the lower edge of the lithographic plate may be inserted in said annular holding space and the heads of said clamps may be inserted in appropriate slots and engaged over the upper margin of said lithographie plate.

7. In a graining machine, a plate holder for holding a lithographie plate or the like, said plate holder comprising a cylindrical sheet having reinforced straight margins, a holding ring secured to the lower margin of said sheet, the upper edge of the ring being offset from the cylindrical sheet to provide an annular holding space, a series of U-shaped clips engaged in said annular space, the upper end of said cylindrical sheet having a series of slots at dierent levels, a series of T-clamps each comprising a shank and a cross piece, each said shank having an abutment and a spring surrounding the shank engaging said abutment, whereby the lower edge of the lithographie plate may be inserted in said annular holding space and the cross piece of said T-clamps may be inserted in appropriate slots and engaged over the upper margin of said lithographie plate.

8. In a lithographie plate graining machine, an upright cabinet having a sump, a blast wheel journaled in said cabinet, said wheel comprising a series of blades and having an open center, a feed pipe having its end communicating with said open center, a slurry pump having an intake conduit communicating with said sump and a discharge conduit communicating with said feed pipe, an elevator cage surrounding said Wheel, said cage having means for supporting a plate to be grained, and means for reciprocating said cage axially of the wheel.

9. In a lithographie plate graining machine, an upright cabinet having a sump, a blast wheel journaled in said cabinet, said wheel comprising a series of blades and having an open center, an upstanding feed pipe projecting up from the sump and having its end communicating with said open center, a slurry pump having an intake conduit communicating with said sump and a discharge conduit communicating with said feed pipe, said feed pipe having a series of stirring pipes having outlets directing streams into said sump to stir the slurry therein, an elevator cage surrounding said Wheel, said cage having means for supporting a plate to be grained, and means for reciprocating said cage axially of the Wheel.

10. In a blasting` machine, an upright, generally cylindrical cabinet having a bottom constituting a sump, a motor housing suspended from the top of the cabinet, an electric motor in said housing having a shaft passing through the bottom thereof, a blast wheel on said shaft, said wheel comprising a series of blades and having an open center, an upstanding feed pipe having its end communicating with said open center, a slurry pump having an intake conduit communieating with said sump and a discharge conduit communicating with said feed pipe, an elevator cage having shoes, guide rails projecting from the inside Wall` of said cabinet on which said shoes ride, means for reciprocating said cage up into the annular space between said motor housing and cabinet wall and down below said sump, a turntable rotatably mounted on said cage, a set of plate holders mounted on said turntable, said plate holders each having means for supporting a plate to be blasted.

11. In a lithographie plate graining machine, an upright, generally cylindrical cabinet having a bottom constituting a sump, a motor housing suspended from the top of the cabinet, said housing having an open top but otherwise being substantially closed, an electric motor in said housing having a depending shaft passing through the bottom thereof, a blast wheel on said shaft, said wheel comprising a series of radial blades and having an open center, an upstanding feed pipe having its end communicating with said open center, a slurry pump having an intake conduit communicating with said sump and a discharge conduit communicating with said feed pipe, said feed pipe having a series of tangentially discharging stirring pipes immersed in the pool of slurry in said sump, an elevator cage having shoes, guide rails projecting from the inside Wall of said cabinet on which said shoes ride, sheaves journaled on the top of said cabinet, lines passing over said sheaves connecting said elevator cage, means connected to said lines for reciprocating said cage up into the annular space between said motor housing and cabinet wall and down to said sump, said cage including a lower supporting ring, rollers rotatably mounted on said ring, a turntable having a track member provided with an annular groove riding on said rollers, a pair of semi-cylindrical plate holders resting on said turntable, said plate holders each having means for supporting a. semicylindrieal plate to be grained.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 469,642 Nehr Feb. 23, 1892 931,341 Phillips Aug. 17, 1909 2,005,654 Fritsche June 18, 1935 2,420,463 Cassin May 13, 1947 2,429,742 Barnes Oct. 28, 1947 2,462,480 Eppler Feb. 22, 1949 

